Do you need space because of the header or the widget ?
To get a bigger modelising space, go to full screen mode.
ACTIVATE the full screen mode
From the header, you can activate the full screen mode.
The "full scree" icon turns green.
DESACTIVATE THE FULL SCREEN MODE
From the header, you can desactivate the full screen mode by clicking again on the corresponding icon.
Tip : you also can use the ESCAPE key of your keyboard